In a programmable DC power supply having a CV mode and a CC mode, modes of operation are implemented with a voltage feedback loop for the CV mode and a current feedback loop for the CC mode, both attempting to regulate their respective parameter to user-specified settings. The DC operating point is determined by a combination of a load line, the large signal voltage-current (V-I) relationship of the load, and either a CV setting or a CC setting, whichever is lower, i.e., whichever setting results in a lower output power level. In the CC and CV modes of operation, the loop that is not regulating opens and relinquishes control to the other loop. Changes in the load may cause the operating point to vary such that the power supply switches modes (CV mode to CC mode or CC mode to CV mode), which is termed mode cross-over.
During a mode cross-over, the loop which was not in control (i.e., open) when the mode cross-over began, seizes control of the supply (i.e., closes) and stabilizes. In an ideal case, the mode cross-over transition is seamless and the supply immediately begins regulating the new parameter. In practice, however, the transition takes a finite amount of time, referred to as mode cross-over latency, during which the operating point may exceed the bounds set by the CV and CC settings. An amount by which the operating point exceeds the set bounds is referred to as mode cross-over overshoot. An amplitude and duration of the mode cross-over overshoots are directly related to a magnitude of the mode cross-over latency.
Conventionally, tracking clamps have been used in an effort to reduce mode cross-over over shoot, however such clamps have a tendency to cause non-linear mode cross-over oscillations (rapid, perpetual switching between CV and CC), making them unusable. These problems have led to the general practice of using a tracking clamp on only one control loop, optimizing mode cross-over overshoots on either the CV to CC, or the CC to CV transition, but not both.